Installation succesfull but I can't login

I have installed succesfully but when i am trying to login I can't do it. I have looked into the tables and I found an user called admin (that is in my system as user system too) with a password. I have tried admin and system password of the user and there is an error. I have even erased this password from the field passwort from sys_user table.
ISPConfig tells about user or password invalid.